Backlight module

ABSTRACT

A backlight module includes a light guide plate, a light source disposed at a side of the light guide plate, a diffuser sheet positioned over the light guide plate but not directly contacting the light guide plate, and a light mixing space positioned between the light guide plate and the diffuser sheet so that light emitted from the light guide plate mixes in the light mixing space before being emitted out of the backlight module.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application is a division application and claims priority ofU.S. patent application Ser. No. 12/616,791, filed on Nov. 12, 2009, nowU.S. Pat. No. 8,408,776, which itself is a continuation application andclaims priority of U.S. patent application Ser. No. 11/755,730, filed onMay 30, 2007, now U.S. Pat. No. 7,658,530, which claims the foreignpriority of Taiwan Pat. application Ser. No. 095145477, the contents ofwhich are hereby incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a backlight module, and moreparticularly to a backlight module comprising a light mixing spacepositioned between a light guide plate and a diffuser sheet.

2. Description of the Prior Art

As quality demands increase rapidly for display devices, LCDs arebecoming a major type of display device, finding wide application innotebooks, personal digital assistants, digital cameras and otherportable electronic products. Because the LCD is a passive illuminatingdisplay device, a backlight module is necessary to provide a lightsource.

A conventional backlight module of an LCD uses a cold cathodefluorescent lamp (CCFL) as the light source. Taking a direct-lightingtype backlight module as an example, a plurality of CCFLs are positionedcollaterally on the bottom of the backlight module to provide aplurality of line-like sources. A diffuser sheet, or a plurality ofoptical films, is placed on the CCFL to provide planar light withuniform brightness. The backlight module with the CCFL as the lightsource is a well developed technology, thus the diffuser and the opticalfilm provide an efficient light source. However, the large size of theCCFL and the high illuminating heat are restrictions of LCDs. Inaddition, the CCFL contains mercury, which causes environment pollution.Therefore, light emitting diodes (LEDs), which have the advantages ofhigh color saturation, quick reaction rate, and small size, are usedwidely in the backlight module as light sources. Research groups arestill working on a backlight module incorporating LEDs for large-sizedLCDs to replace the conventional cold cathode fluorescent lamp. Becausethe color saturation of white LEDs still needs to be improved, red LEDs,green LEDs, and blue LEDs are used together as the white light source inthe backlight module. In this situation, a design with good light mixingis important for making the red, green, and blue light mix well.Therefore, the backlight module incorporating LEDs has a morecomplicated structure and higher price than a traditional backlightmodule incorporating CCFLs.

FIG. 1 shows a side view of a conventional backlight moduleincorporating LEDs. The backlight module 10 is a direct-lighting typebacklight module applied to large size LCDs, such as a flat panel TVs.The backlight module comprises a frame 12, a diffuser sheet 20positioned on the frame 12, and a plurality of top-emitting LED sources14 positioned in the frame 12 and soldered on a printed circuit board(PCB) 18. The LED source 14 comprises a red LED, a blue LED, and a greenLED positioned uniformly in the frame 12. After mixing the red, blue,and green light properly, a white light source can be provided. Inaddition, the conventional backlight module further comprises areflective sheet 16 or reflective material positioned on the PCB 18. Thethickness of a backlight module of a flat panel TV is approximately 2cm. Therefore, in order to achieve uniform brightness, higher numbers ofLED sources 14 with smaller current, such as 20 mA, are positioned inthe backlight module 10. In this design, the light emitted by the LEDsources 14 illuminates the luminous face of the backlight module 10directly, so the light utility efficiency is higher and the heatdissipation is better, because the LED sources 14 are positioneduniformly. However, the increased number of LED sources 14 increases thecost of the backlight module 10. In addition, according to thestructural design of the backlight module 10, the light cannot mix well.Furthermore, only a specific wavelength range or power of the red LED,blue LED, and green LED can be used in the LED source 14.

The conventional backlight module can also include a lower number ofhigh-power LEDs, such as 350 mA LEDs, combined with special designprisms positioned on the surface of the LED to provide the light source.However, this design increases the thickness of the backlight module,and fans, heat pipes, or other heat dissipation devices are needed tohelp heat dissipation, so the cost is increased. In addition, specialdesign prisms are usually patented, so the product cost of the backlightmodule is also increased.

As demonstrated in the above, designing an LED backlight module with lowcost and good light mixing function is an important task for thebacklight module industry.

SUMMARY OF THE INVENTION

It is therefore an objective of the present invention to provide abacklight module with a light mixing space and at least a light guideplate to solve the abovementioned problems.

The backlight module, according to the present invention, comprises alight guide plate; a light source positioned at a side of the lightguide plate; a diffuser sheet positioned on the light guide plate; and amixing space positioned between the light guide plate and the diffusersheet. The light guide plate comprises a light-exit face and at least alight-incidence face. The light emitting from the light source entersthe light guide plate from the light-incidence face. The diffuser sheetdoes not contact the light guide plate and the light source. Inaddition, the mixing space is positioned between the light guide plateand the diffuser sheet, so the light passing through the light-exit facecan be mixed sufficiently in the light mixing space before being emittedfrom the backlight module.

The backlight module of the present invention comprises a light guideplate and the light source is positioned at a side of the light guideplate, so the light can be distributed properly through the light guideplate. Furthermore, the backlight module in the present inventioncomprises a light mixing space positioned between the light guide plateand the diffuser sheet to make the light mix sufficiently in the lightmixing space before being emitted the backlight module so the whitelight with better color saturation can be generated.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a side view of the conventional backlight moduleincorporating LEDs.

FIG. 2 depicts a side view of the backlight module in the firstembodiment of present invention.

FIG. 3 depicts a top view of the backlight module in FIG. 2.

FIG. 4 shows a schematic diagram of the second embodiment of thebacklight module of the present invention.

FIG. 5 shows a schematic diagram of the third embodiment of thebacklight module of the present invention.

FIG. 6 shows a schematic diagram of the fourth embodiment of thebacklight module of the present invention.

DETAILED DESCRIPTION

The backlight module of the present invention can be applied to LCDs orother display devices that require a light source. FIG. 2 depicts a sideview of the backlight module in a first embodiment of the presentinvention while FIG. 3 depicts a top view of the backlight module inFIG. 2. The backlight module 50 in the present invention is adirect-lighting type, and can be applied to small-, medium-, andlarge-size LCDS. The backlight module 50 comprises a frame 52, aplurality of light guide plates 56 positioned in parallel at the bottomof the backlight module 50, alight source 54, a diffuser sheet 60, and alight mixing space 62. The frame 52 comprises at least four sidewallsforming a containing space 64 to hold the light source 54, the lightguide plate 56, and the diffuser sheet 60.

Every light guide plate 56 comprises a light-incidence face 68 and alight-exit face 70 connected to each other perpendicularly, and thesurface of each light guide plate 56 comprises a plurality of lightguide patterns to guide light toward the light-exit face 70. Thediffuser sheet 60 is positioned over the light guide plate 56 withoutcontacting the light guide plate and the light source. The light source54 is a point light source or a directional light source, such as a 100mA LED, positioned next to a side of the light guide plate 56 to makethe light emitting from the light source 54 enter the light guide plate56 from the light-incidence face 68 and exit from the light-exit face 70after scattering. Referring to FIG. 3, in this embodiment, the lightsource 54 comprises red LEDs 54 a, green LEDs 54 b, and blue LEDs 54 cdisposed alternately and in parallel on a side of the light-incidenceface 68 of the diffuser sheet 54. However, the light source 54 can alsobe a white light source.

In addition, the light mixing space 70 is in a part of the containingspace 64 surrounded by the diffuser sheet 60, the light source 54 andthe light guide plate 56. This means that the light passing through thelight-exit face 70 can be mixed sufficiently in the light mixing space62 before being emitted from the backlight module 50 through thediffuser sheet 60. The backlight module 50 can further comprise areflective sheet 58 positioned under the light source 54 and the lightguide plate 56, in order to reflect the light proceeding to the bottomof the backlight module 50, such that the light utility efficiency isincreased. In other embodiments, a plurality of optical films (notshown), such as prisms or brightness enhancement films (BEF), can bepositioned on the diffuser sheet 60 to increase the brightness of thelight provided by the backlight module.

As shown in FIG. 2, the light guide pattern 66 can be a V-shaped type ora U-shaped type positioned at the bottom of the light guide plate 56 toreplace the BEF and making the light gather toward the light-exit face70. However, the light guide pattern 66 can also be a printing pattern,a sandblasting pattern or a dot injection molding pattern to influencetotal reflection of the light guide plate 56 to make the light proceedtoward the light-exit face 70. In addition, the light guide pattern 66can also be positioned partly on a different surface of the light guideplate 56, such as the surface of the light-exit face 70, to adjust thebrightness distribution of the light leaving the light guide plate 56.

It should be noted that the arrow points show the main route of thelight emitting from the light source 54 in the light guide plate 56. Byspecial design of the light guide pattern 66, most of the light will begathered to specific regions (shown by dotted lines in FIG. 3) on thelight-exit face 70 before leaving the light guide plate 56. Because thelight focuses on specific regions of the light-exit face 70, the lightleft from the light guide plate 56 will form a plurality of line-likeline sources 72, 74 and the light source provided by the LEDs 50 a, 50b, 50 c will look like the light source provided by the conventionalcold cathode fluorescent lamp. The number of the line-like line sources72, 74 depends on the actual size of the display. In addition, in otherembodiments, the light guide plate 56 of the backlight module 50 canalso be strip-shaped, so that the light-exit face 70 is strip-shaped,making the light emitted from the light guide plate 56 forms a line-likeline source. Furthermore, because the backlight module 50, according tothe present invention, can provide light similar to the linear lightprovided by the conventional cold cathode fluorescent lamp (CCFL), thediffuser sheet 60 or other optical films in the backlight module 50 cankeep the conventional design used in the backlight module thatincorporates CCFLs, and therefore research and development costs arespared.

Because the light source 54 in the present invention is a directionallight source, the light enters and is emitted from a side of the lightguide plate 56. In contrast, the upper region of the light source 54does not have any light emission, so dark areas may occur. However, thelight mixing space 62 provides uniform brightness of light, includingthe upper region of the light source 54, by mixing the light emittedfrom the light guide plate 56 sufficiently before entering the diffusersheet 60.

Because the LED light source 54 in the present invention has higherpower than the conventional LED light source, a lower number of LEDlight sources 54 achieve the same illuminating effect of theconventional LED light source so that the packing cost is decreased. Inaddition, the heat dissipation ability of the backlight module 50 in thepresent invention is better than the conventional high power LEDbacklight module. Furthermore, the mixing effect can be improved bypositioning the diffuser sheet 56 at a side of the LED source 54, thusthe range of wavelength and brightness that can be used for the lightsource is expanded. The light source 54 design can also have morevariety.

FIG. 4 shows a schematic diagram of a second embodiment of the backlightmodule of the present invention. In FIG. 4, the same number numerals asFIG. 3 designate similar or the same parts, regions or elements. In thisembodiment, the light source 54 is a double-emitting light sourcepositioned between two adjacent light guide plates 56, 57. Thelight-incidence faces 68, 69 of the light guide plates 56, 57respectively are positioned on two sides of the light source 54 to guidethe light emitted from the light source 54 to enter the light guideplate 56, 57 from the light-incidence faces 68, 69 of the light guideplates 56, 57. Furthermore, the light enters the light-incidence faces68, 69 will pass through the light-exit faces 70, 71 respectively. Theadvantage of the present invention is that by using the double-emittinglight source, the number of light sources can be decreased, and heatdissipation ability is increased. Furthermore, the space of the deviceis spared and electricity consumption is reduced.

In other embodiments, the light guide plate 56 can comprise twolight-incidence faces 68 at the same time, and a light source 54 can bepositioned at two sides of the light guide plate 56, so that the lightcan enter the light guide plate 56 from the different light-incidencefaces 68, thus increasing the brightness.

FIG. 5 shows a schematic diagram of a third embodiment of the backlightmodule of the present invention. The backlight module 100 comprises aframe 102 forming a containing space 114, at least two light guideplates 106, a light source 104 positioned at a side of the light guideplates 106, a reflective sheet 108 positioned under the light source 104and the light guide plates 106, a diffuser sheet 110 positioned on thelight source 104 and the light guide plates 106, and a light mixingspace 112 surrounded by the diffuser sheet 110, the light source 104 andthe light guide plates 106. The preferred light source in the presentinvention is a point light source, and a better light source is atop-emitting LED positioned on a PCB. Therefore, the light guide plates106 are a little higher than the light source 104, and thelight-incidence face 118 is positioned at a side of the light guideplates 106, which is parallel to the light-exit face 120. Thus, thelight emitted from the top of the light source 104 can enter the lightguide plates 106 from the light-incidence face 118 directly. Every lightguide plate 106 can further comprise a reflective face 122 to reflectthe light emitting from the light source 104 laterally toward the wholelight guide plate 106, and the reflected light passing through thelight-exit face 120 will become a plurality of line-like sources (asshown by the arrow in FIG. 5). Furthermore, an obtuse angle θ ispositioned between the reflective face 122 and the light-exit face 120.However, the light guide plate 106 can be designed to let a little lightemit into the upper part of the light guide plate 106 by using thereflective face 122 to adjust the light mixing effect and also improvethe dark area problem. In this embodiment, a plurality of light guidepatterns can be positioned on the surface of light guide plates 106 toadjust the direction of the light. For example, the light guide patternscan be a V-shaped type or U-shaped type or printing patterns,sandblasting patterns or dot injection molding positioned on the top orbottom surface of the light guide plate. Sandblasting patterns or dotinjection molding can focus the light to form line-like sources. Thearrow points show the route of light proceeding through the light guideplate 106. Most of the light focuses on several regions of the lightguide plate 106 and forms line-like sources.

Furthermore, the backlight module 100 may comprise supporting structures124 of a same number as the light guide plates 106. The supportingstructures 124 are positioned under the light guide plates 106, and thethickness of the supporting structures 124 may be approximately largerthan the height of the light source 104, so as to hold the light guideplate 106 a little higher than the light source 104. In addition, toincrease the light utility efficiency, the preferred supportingstructure 124 can have a reflective function to reflect the lightemitted from the bottom of the light guide plate 106 back to the insideof the light guide plate 106 or to the light mixing space 112.

FIG. 6 shows a schematic diagram of a fourth embodiment of the backlightmodule of the present invention. In FIG. 6, the same reference numeralsin FIG. 5 designate similar or the same parts, regions or elements. Inthis embodiment, the thickness of the light guide plate 106 is thickerthan the light source 104, which is different from the third embodiment.The thicker light guide plate 106 replaces the supporting structure 124of the third embodiment. The light guide plate 106 has a recessed space126 positioned at a bottom side of the light guide plate 106, and thesize of the recessed space 126 corresponds to the size of the lightsource 104 to hold the light source 104. Therefore, the light source 104is buried in the light guide plate 106 and at least four sides of thelight source 104 contact the surface of the recessed space 126.Furthermore, the light emitted from the top or the side of the lightsource 104 can illuminate the light guide plate 106 through the surfaceof the recessed space 126. So, the light source of this embodiment canbe a top-emitting LED or a side-emitting LED, and the light-incidenceface 118 of the light guide plate 106 can be positioned on any surfaceof the corresponding recessed space 126.

As mentioned above, the backlight module in the present inventioncomprises a plurality of point light sources, such as LEDs, disposed ata side of one or several light guide plates. Thus, the number of lightsources can be decreased. In addition, the light guide patternspositioned on the light guide plate can change the point light source inthe present invention into a line-like source by adjusting thebrightness distribution on the light-exit face. By imitating thebrightness distribution of the cold cathode fluorescent lamp, the LEDbacklight module in the present invention has the same effect as theconventional cold cathode fluorescent lamp, but it has lower cost,better heat dissipation, and is more environmentally friendly. Moreover,the conventional diffuser sheets and optical films used for cold cathodefluorescent lamps can still be applied to the backlight module in thepresent invention. Thus, research and development costs are spared.Finally, the light mixing space in the present invention makes the lightmix sufficiently before entering the diffuser sheet to provide a uniformplanar light source.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A backlight module comprising: a light guideplate having a light-exit face and at least one light-incidence face,wherein the light-incidence face and the light-exit face of the lightguide plate are opposed to each other collaterally; a light sourcepositioned at a side of the light guide plate, wherein light emittedfrom the light source enters the light guide plate from thelight-incidence face; a diffuser sheet positioned on the light guideplate without contacting the light guide plate and the light source, thediffuser sheet being parallel to the light-exit face of the light guideplate; and a light mixing space disposed between the diffuser sheet andthe light guide plate wherein the light passing through the light-exitface mixes in the light mixing space before being emitted from thebacklight module.
 2. The backlight module of claim 1, wherein the lightguide plate comprises at least a recessed space to hold the lightsource.
 3. The backlight module of claim 1, further comprising asupporting structure positioned under the light guide plate to hold thelight guide plate higher than the light source.
 4. The backlight moduleof claim 3, wherein the supporting structure comprises a reflectiveelement.
 5. The backlight module of claim 1, wherein the light guideplate is strip-shaped to make the light passing through the light guideplate become a line-like source.
 6. The backlight module of claim 1,wherein the light guide plate comprises a plurality of light guidepatterns to guide the light toward the light-exit face, and make lightpassing through the light-exit face become a plurality of line-likesources.
 7. The backlight module of claim 6, wherein the light guidepattern is a V-shaped type or a U-shaped type.
 8. The backlight moduleof claim 1, further comprising a reflective sheet positioned under thelight source and the light guide plate.
 9. The backlight module of claim1, further comprising a frame comprising a containing space to hold thelight source, the light guide plate and the diffuser sheet, wherein theportion of the containing space surrounded by the light source, thelight guide plate and the diffuser sheet forms the light mixing space.10. The backlight module of claim 1, wherein the light guide platecomprises a reflective face to reflect the light entering the lightguide plate laterally and make light passing through the light-exit facebecome a plurality of line-like sources, and an obtuse angle is betweenthe reflective face and the light-exit face.